Fix -Wunreachable-code-break error

Remove some spurious break statements that
https://pdfium-review.googlesource.com/123810 recently added. The
warning did not trigger in PDFium builds due to a viral
-Wno-unreachable-code-break from Abseil, which assumes all non-Chromium
projects want to suppress that warning.

Change-Id: I1bab5ed6849160c48b7dd2790a08664852ba96db
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/123910
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@google.com>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

fpdfsdk/cpdfsdk_helpers.cpp

diff --git a/fpdfsdk/cpdfsdk_helpers.cpp b/fpdfsdk/cpdfsdk_helpers.cpp
index 8252007..c1cf7d4 100644
--- a/fpdfsdk/cpdfsdk_helpers.cpp
+++ b/fpdfsdk/cpdfsdk_helpers.cpp
@@ -218,13 +218,10 @@
   switch (format) {
     case FPDFBitmap_Gray:
       return FXDIB_Format::k8bppRgb;
-      break;
     case FPDFBitmap_BGR:
       return FXDIB_Format::kBgr;
-      break;
     case FPDFBitmap_BGRx:
       return FXDIB_Format::kBgrx;
-      break;
     case FPDFBitmap_BGRA:
       return FXDIB_Format::kBgra;
     default: